1. Field to the Invention
The present invention relates to a golf club shaft and more particularly to a golf club shaft which gives a golfer preferable feeling when the golfer swings and which is improved in the flight distance of a golf ball and a flight direction thereof.
2. Description of the Related Art
If the shaft is soft, i.e., if the flexure amount of the golf club shaft is set large, the golfer has a feeling that the shaft is flexible and obtains a soft feeling when the golfer hits the golf ball. Further the soft shaft has an advantage that the golf ball can fly a long distance owing to the restoring force of the flexed shaft. On the other hand, if the shaft is soft, the golfer feels that the shaft is unreliable and the flight direction is not uniform because the flexure amount is large.
On the other hand, if the shaft is hard, i.e., if the flexure amount of the golf club shaft is set small, the golfer has a feeling of stiffness. Thus the golfer can swing powerfully with a feeling of safety. Further the hard shaft allows both the flight distance of a golf ball and its flight direction to be uniform. However, the golfer does not feel that the shaft is flexible. That is, the golfer feels that the shaft is hard and cannot flex it sufficiently when the golfer hits the golf ball, which causes the flight distance of the golf ball to be shorter.
As described above, to give “feeling of flexibility” to the golfer and increase a “flight distance” by making the shaft soft is reciprocal to give “feeling of stiffness” to the golfer and make the flight direction uniform by making it hard. Therefore, various proposals have been made to make the “feeling of flexibility” and the “feeling of stiffness” compatible with each other and increase of the “flight distance” and the stability of the “flight direction” compatible with each other.
For example, in Japanese Patent Application Laid-Open No. Hei 9-234256, there is disclosed a golf club shaft having the region having a high torsional rigidity at the grip part thereof and the front end (head) and the region having a high flexural rigidity in the center thereof. In Japanese Patent Application Laid-Open No. Hei 10-127838, there is disclosed a golf club shaft having the region having a maximum flexural rigidity not at the grip part but at the front end (head).
In Japanese Patent Publication No. 2705047, there is disclosed a golf club shaft having reinforcing layers of different lengths layered one upon another, with the ends of the reinforcing layers coincident with one another in the rear end (grip side) of the shaft. The ends of the wound fiber reinforced synthetic resinous sheets are butted on each other to make the rigidity of the shaft uniform in its circumferential direction. In Japanese Utility Model Application Laid-Open No. Hei 6-7764, there is disclosed a golf club shaft having a plurality of reinforcing layers having different lengths so constructed as to increase the rigidity of the shaft toward the grip side thereof.
However, in the golf club shaft of Japanese Patent Application Laid-Open No. Hei 9-234256, because the shaft has the high flexural rigidity in its central portion, a sufficient degree of flexibility cannot be obtained. Further because the behavior of the shaft during swinging is different from that of the conventional shaft, the shat has a problem that a golfer has difficulty in taking a timing.
In the golf club shaft disclosed in Japanese Patent Application Laid-Open No. Hei 10-127838, because the region having the maximum flexural rigidity is formed not at the grip side but at the front end (head), and attention is not paid to the rigidity of the grip part, the grip part has a low rigidity and is liable to deform when the golfer swings. Thus when the golfer swings, the golfer cannot have feeling of security or swing with all the golfer's might. Further the it is difficult for the golfer to swing in an uniform style. There is no disclosure of the layered construction of a fiber reinforced prepreg composing the shaft. It is necessary to provide the golf club shaft with a complicated layered construction of the fiber reinforced prepreg to form the region having the maximum flexural rigidity not at the grip part but at the front portion (head) of the golf club shaft. In this case, there is a restriction in the manufacture of the golf club shaft.
Both the golf club shaft disclosed in Japanese Patent Publication No. 2705047 and that disclosed in Japanese Utility Model Application Laid-Open No. Hei 6-7764 have a smaller outer diameter than that of the conventional golf club shaft. Because no attention is paid to the rigidity of the golf club shaft at its head side, the golf club shaft lacks stability in the flight direction of the golf ball. These golf club shafts have another problem that much consideration is not taken for the golfer's feeling. That is, the golfer has an uncomfortable feeling when the golfer hits the golf ball.